HashiCorp Vault is an open-source tool for securing, storing, and tightly controlling access to secrets and sensitive data in modern computing environments. One of Vault's key mechanisms for securely protecting these secrets is known as Shamir's Secret Sharing, an algorithm that splits data into parts, called shares, and only reconstructs the data when a certain number of shares are combined.

Unfortunately, prior to the release of Vault versions 1.13.1, 1.12.5, and 1.11.9, the implementation of Shamir's Secret Sharing was discovered to be vulnerable to cache-timing attacks due to its use of precomputed table lookups. In this post, we will delve into the vulnerability's details, briefly explain Shamir's Secret Sharing, and discuss how this critical security issue was addressed in the latest updates.

Background on Shamir's Secret Sharing

Invented by Adi Shamir in 1979, Shamir's Secret Sharing is an algorithm for securely splitting data into multiple parts, each of which constitutes a "share." The secret (i.e., the data being protected) can only be reconstructed when a certain predetermined number of shares are combined. This threshold is defined by the user and is denoted as "k," while the total number of shares created is denoted as "n."

The mathematical foundation for Shamir's Secret Sharing comes from polynomial interpolation, specifically utilizing the concept of Lagrange polynomials. Simply put, given k-1 shares, an attacker cannot gain any knowledge about the secret; however, upon obtaining the k-th share, the attacker can fully reconstruct the secret.

Vulnerability Details

The vulnerability (CVE-2023-25000) in HashiCorp Vault's implementation of Shamir's Secret Sharing arises due to the use of precomputed table lookups. By observing cache-timing patterns on a host during unseal operations, an attacker with access to the host and the ability to observe a large number of unseal operations could potentially reduce the search space of a brute force effort, increasing the chances of recovering the Shamir shares.

The precomputed table lookups, in combination with the cache-timing patterns, could enable an attacker to apply machine learning techniques and side-channel information to predict sensitive information about the unsealing process. This effectively weakens the security of the Shamir Secret Sharing implementation in Vault, making it possible for an attacker to obtain the shares needed to reconstruct the secret.

Fixes and Patches

To address this vulnerability, HashiCorp released Vault versions 1.13.1, 1.12.5, and 1.11.9. The updated implementation removes the reliance on precomputed table lookups and mitigates the cache-timing side-channel risk. Vault operators are highly encouraged to upgrade to the fixed versions as soon as possible to secure their sensitive data and secrets.

Original References

1. HashiCorp Vault Official Website
2. Shamir's Secret Sharing
3. Vault's Security Update

In conclusion, the CVE-2023-25000 vulnerability in HashiCorp Vault's implementation of Shamir's Secret Sharing underscores the importance of staying up-to-date with patches and security fixes for critical software components. By upgrading to the latest released versions (1.13.1, 1.12.5, or 1.11.9), Vault users can help safeguard their sensitive data from potential cache-timing attacks and ensure the integrity of their secret-sharing mechanisms.

Timeline

Published on: 03/30/2023 01:15:00 UTC
Last modified on: 04/06/2023 14:45:00 UTC